My thoughts are that the title is a wee bit misleading, don't you think?
No one was "American" back then, other than the natives.
Dr Ian Tomlinson, Molecular and Population Genetics Laboratory, London Research Institute, Cancer Research UK has not observed this specific mutation in English patients today, suggesting that the couple that immigrated to America around 1630 were indeed the founders of the genetic change and that, if any British relatives had the mutation it may have helped to extinguish that line.